In this paper, we present the design of a low-profile antenna consisting of two orthogonal parasitic meandered monopoles excited by the near-filed coupling with a feeding bow-tie. The two parasitic radiators and the driven element are placed on two different faces of the same dielectric substrate and a coaxial probe excites the bow-tie through a metallic ground plane. In this way, the antenna has compact dimensions of 21×10.5×1.6 mm³(λ₀/6×λ₀/12×λ₀/75, excluding the ground plane) and exhibits a good impedance matching in the 2.4-2.485 GHz Wi-Fi band with an overall efficiency around 50%.

Underground mines are challenging environments for off-body wireless communication, since the signal propagation is majorly affected by small scale and large scale fading. The use of multiple antennas at the transmitter and the receiver sides is a known technique to combat fading and enhance capacity. In this paper, the channel parameters of a 2×2 Multiple-Input Multiple-Output (MIMO) off-body system are investigated in an underground gold mine and compared to the Single-Input Single-Output (SISO) system parameters. Measurement campaigns were conducted using monopole antennas at a center frequency of 2.45 GHz for both Line Of Sight (LOS) and None Line of Sight (NLOS) scenarios. The measured frequency responses are converted into impulse responses through an Inverse Fourier Transform (IFT). The results show that for a constant transmitted power, the path loss exponents at NLOS are smaller than their counterpart values at LOS. The channel capacity values decrease as the propagation distance increases and when the link is obstructed at NLOS. The RMS delay spread is generally increasing with distance for both LOS and NLOS situations. When a fixed Signal-to-Noise Ratio (SNR) is assumed, MIMO topologies improved the SISO capacity by roughly 8 bps/Hz. The channel characterization results demonstrate that the MIMO configurations provided a remarkable improvement in terms of capacity, coherence bandwidth, and time delay spread compared to the SISO topologies.

Sparse representation is the fundamental technology of compressive sensing, sparse three-dimensional (3-D) imaging, and dictionary-based parameter estimation. Typical sparse representation models of radar signal work in the frequency domain, which may encounter high dimension and large data amount of dictionary. This paper presents a time-domain (TD) representation model for multi-aspect SAR data. We generate the multi-aspect two-dimensional (2-D) TD responses of the 3-D scattering center model. Then we cut off the low-energy area of the 2-D TD response and use cutoff responses to construct the dictionary of sparse representation. Such a TD dictionary is a sparse matrix. Moreover, we build and solve the sparse representation model based on the TD dictionary. Compared with the frequency-domain (FD) sparse representation model, the data size of our TD dictionary is remarkably lower, and the solving of TD sparse representation problem is in higher efficiency. We utilize the TD sparse representation to reconstruct 3-D images from multi-aspect SAR data. Experimental results demonstrate the effectiveness and efficiency of the TD sparse representation model.

Evanescent mode substrate integrated waveguide (SIW) is one of the promising technologies for design of light-weight low-cost microwave components. Traditional realization methods used in the standard evanescent waveguide technology are often not directly applicable to SIW due to dielectric filling and small height of the waveguide. In this work, one of the realization methods of evanescent mode waveguides using a single layer substrate is considered. The method is based on the use of coaxial stubs as capacitive susceptances externally connected to a SIW. A microwave filter based on these principles is designed, fabricated, and tested. The filter exhibits a transmission zero due to the implemented stubs. The problem of evanescent mode filter analysis is formulated in terms of conventional network concepts. This formulation is then used for modelling of the filters. Strategies to further miniaturization of the microwave filter are discussed. The approach is useful in applications where a sharp roll-off at the upper stop-band is required.

We describe a technique to analytically compute the multipole moments of a charge distribution confined to a planar triangle, which may be useful in solving the Laplace equation using the fast multipole boundary element method (FMBEM) and for charged particle tracking. This algorithm proceeds by performing the necessary integration recursively within a specific coordinate system, and then transforming the moments into the global coordinate system through the application of rotation and translation operators. This method has been implemented and found use in conjunction with a simple piecewise constant collocation scheme, but is generalizable to non-uniform charge densities. When applied to low aspect ratio (≤100) triangles and expansions with degree up to 32, it is accurate and efficient compared to simple two-dimensional Gauss-Legendre quadrature.

A theoretical analysis of numerical dispersion in the high-order finite-difference time-domain (FDTD) method with weighted Laguerre polynomials (WLPs) is proposed in this paper. According to the numerical dispersion relation for the two-dimensional (2-D) case, the numerical phase velocities relevant to the direction of wave propagation, grid discretization and time-scale factor are obtained. For a fixed relative error of the numerical phase velocity, the suitable sampling point density and time-scale factor can be determined. Compared with the low-order WLP-FDTD, the high-order one shows its good dispersion characteristics while a low sampling density is used. Three numerical examples are included to validate the effectiveness of the high-order scheme.

A compact coplanar waveguide-fed tri-band monopole antenna for WLAN/WiMAX applications is proposed. By employing a pair of inverted-L slots etched on the ground plane and a split-ring resonator (SRR) and further carefully adjusting the lengths and positions of these structures, two notched bands can be obtained. Measured results show that a tri-band of 280 MHz (2.28-2.56 GHz), 920 MHz (3.29-4.21 GHz), and 860 MHz (5.05-5.91 GHz) with reflection coefficient less than -10 dB is obtained covering all the 2.4/5.2/5.8 GHz WLAN bands and 3.5/5.5 GHz WiMAX bands. In addition, good dipole-like radiation characteristics over the required bands is achieved in both E- and H-planes.

In this paper, two planar diplexers using dual-mode resonators are designed, which have achieved significant size miniaturization. The first diplexer is made of a simple single dual-mode resonator as a square cavity in the substrate integrated waveguide technology. The two degenerate modes with 90° rotation are perturbed by the placement of metallic via and CPW lines as input and output ports. A prototype model of this diplexer is designed and fabricated in the X-band. Its simulation results and measurement data agree very well. An isolation of 22 dB is achieved between two ports, which is quite suitable for receiving systems. For the improvement of isolation and bandwidth, the degree of structure is increased, whereby dual-mode resonators are used to connect the channel filters to the input port. Those types of channel filters are used which generate a transmission zero in the frequency band of the other channel. The isolation and bandwidth of the diplexer have been improved significantly, where its size is much smaller than the common diplexers.

Double-sided open periodic structures are analyzed using inhomogeneous plane wave scattering. The leaky and surface wave modes of several unit cells of different structures are computed using the poles of generalized reflection and transmission coefficients of inhomogeneous plane waves in the spectral domain. It is shown that the reflection and transmission coefficients of the zeroth order Floquet mode contain the poles of the Green's function of the complex stratified periodic structure. The properties of evanescent mode amplification as well as super resolution near field imaging in a wire medium are addressed. A balanced leaky wave antenna unit cell with double-sided radiation feature is introduced and it is shown that, in contrast to grounded structures, total absorption in lossless non-chiral double-sided open unit cells is not feasible as long as the behavior of the unit cell is well described by its fundamental mode.

New designs of all-optical logic gates based on spatial-soliton interactions in optical communication spectral regions were proposed. The proposed structures are composed of local nonlinear Mach-Zehnder interferometer (MZI) waveguide structures with multi-input ports and two nonlinear output ports. They can be used to design various all-optical logic gates. The nonlinear MZI waveguide structure with local nonlinear waveguides functions like a phase shifter. It employs angular deflection of spatial solitons controlled by the phase modulation created in the local nonlinear MZI. The light-induced index changes in the local nonlinear MZI waveguide structures break the symmetry of structure and make the output signal beam propagate through different nonlinear output waveguides. By properly choosing the input control power, the spatial solitons will be switched to different output ports. The numerical results show that the proposed local nonlinear MZI waveguide structures could really function as all-optical logic gates in the optical communication spectral region.

A novel multi-band cylindrical dielectric resonator antenna (CDRA) using microwave laminates with permittivity variation in azimuth direction fed by coaxial probe is proposed in this paper. The proposed structures are constructed using different materials having different permittivities in azimuth direction in cylindrical dielectric resonator (DR). In order to determine the performance of various design parameters on resonance frequency and bandwidth, parametric studies have been performed. The operating band can be scaled up or down by adjusting the design parameters. Dualband and triple-band CDRAs have been fabricated using commercially available microwave laminates to validate the simulation results. For each case, the input reflection coefficient, radiation pattern and antenna gain are simulated and measured. Good agreement between simulated and measured results has been observed. The proposed antennas may be suitable for WLAN applications.

Two new microstrip tri-mode modified ring resonators (Resonator A and Resonator B) are presented and discussed through mode analysis method. The characteristic difference between these two resonators is that the center frequency of the tri-mode Resonator B is still the same as that of traditional dual-mode ring resonator, while the center frequency of Resonator A will be shifted up compared with that of traditional ring resonator. Based on these two novel resonators, two bandpass filter examples are designed, fabricated and measured. The simulations and measurements are in good agreement which validate the design ideas.

In this paper, we present an equivalent current-based numerical routine for calculating the diffraction of arbitrarily curved wedge modeled with non-uniform rational B-spline (NURBS) curves and surfaces. The NURBS curves and surfaces obtained from CAD systems need to be parameterized for numerical calculation; however, available parameterizing approaches in rendering computer graphics, which use straight line segments and flat facets for tessellation, are not suitable for the computation of the wedge diffraction. To make the full use of NURBS modeling technique in high-frequency asymptotic approaches, the proposed numerical routine utilizes a curvature adaptive tessellation scheme to parameterize the edge curve of the wedge with varying curvature as well as the method of parameter alignment to maintain the C0 continuity between the edge curve and the wedge surfaces, which is essential in evaluating the diffraction coefficients. Based on the proposed parameterizing method, the equivalent edge current can be implemented for diffraction computation of arbitrarily curved wedge modeled with NURBS curves and surfaces, complementing with the NURBS based physical optics (PO) as a fully NURBS-based high-frequency approach, which provides high geometrical accuracy and computational efficiency for calculating diffraction of electrically large curved wedges. Numerical examples are presented to validate the proposed method.

We investigate the problem of near field interactions with general antenna systems using the antenna current Green's function formalism recently proposed by the authors as a framework for the theoretical and computational analysis of the interaction problem. The paper focus is on conceptual and numerical issues related to the analysis of the electromagnetic response of generic devices to arbitrary illumination fields produced, for example, by nearby source or scattered by surrounding objects. We provide some method of moment numerical examples involving wire antenna systems substantiating the ACGF approach to the problem of near field excitations.

In this paper, a dual-band Substrate Integrated Waveguide (SIW) resonator with Sierpinski fractal geometry is proposed. The space-filling property of the employed fractal shape allows to reduce the resonator size. The bandwidth, the minimum insertion loss, the maximum return loss and the stop band rejection are considered for evaluating the effect of the fractal geometry on the resonator characteristics. An accurate electromagnetic investigation is made using a full wave finite element method solver (Ansoft HFSS). Simulated and measured results are in good agreement. The second iteration fractal resonator exhibits two simulated bands centered at the frequencies f₁=11.57 GHz and f₂=25.7 GHz, while the measured frequencies are f₁=11.33 GHz, f₂=23.67 GHz. The measured bandwidths are BW=1.15 GHz and BW=2 GHz and the minimum insertion losses are close to -1.36 dB and -1.97 dB, respectively. The prototypes of the square resonator without, with first and with second iteration fractal geometry are fabricated via standard printed circuit board process (PCB). A Rogers Duroid 5880 substrate with thickness t=0.381 mm is employed.

The concept of Scattering-Induced Mutual Coupling Effect (SIMCE) is proposed, and the mechanism of producing this phenomenon in Multiple-Input Multiple-Output (MIMO) communication systems at MilliMeter Wave (MMW) band is demonstrated. The model of estimating the scattering-induced mutual impedance in rain environment is derived, and the characteristics of Rain-Induced Scattering Mutual Impedance (RISMI) are discussed taking parabolic antennas as an example. The model of estimating the rain-induced mutual impedance is helpful for investigating the SIMCE in other discrete random media. And, the results given in this paper are significant for developing MMW MIMO communication systems.

This paper presents an effective joint range-DOA-frequency (JRDF) estimation method based on fourth-order cumulants for multiple mixed near-field sources and far-field sources impinging on a symmetric uniform linear array, named as JRDF algorithm. Making use of the proposed method, range-DOA-frequency can be effectively estimated by the same eigen-pair of a defined ``information matrix'' constructed by two fourth-order cumulant matrices. Compared with the related works, the proposed method can provide superior performance, such as higher estimation accuracy, without the procedure of parameter search or parameter matching. Simulation results are presented to demonstrate the efficacy of the proposed approach.

Based on the Collins integral formula and Lohmann optical system, we expand the hard edge aperture into complex Gauss function and derive an approximate analytic expression of intensity distribution theoretically for Hypergeometric-Gauss beams through the fractional Fourier transform (FRT) optical systems with hard edge aperture. The influences of FRT order, aperture size and other optical parameters on the light intensity distribution of Hypergeometric-Gauss beams passing through the FRT optical systems are discussed in detail. The results show that the FRT is an excellent beam-shaping method.

We have studied the instability of electrostatic ion-cyclotron waves in collisional magnetized two-ion component plasma (light positive K⁺ ions and heavy positive Cs⁺ ions). An ion beam propagating through collisional magnetized plasma containing electrons and two positive ion components drives electrostatic ion cyclotron (EIC) waves to instability via Cerenkov interaction. Analytical expressions & numerical calculations have been carried out for the frequency and growth rate of ion cyclotron waves for two EIC wave modes for existing experimental parameters, and it is found that the unstable mode frequency does not depend on electron collision frequency, while the growth rate is increased linearly with the electron collision frequency. Moreover, as the light ion concentration is increased, the frequency of the heavy ion mode moves closer to its gyrofrequency. Similarly, the frequency of the light ion mode approaches the light ion cyclotron frequency as the heavy ion concentration is increased. It is also found that the normalized unstable mode frequencies remains unchanged with electron collision frequencies, while the growth rate is increased linearly with the electron collision frequencies. In addition, the unstable mode frequencies are found to be dependent on the magnetic field strengths.

In this paper, a compact microstrip fed ultra-wideband antenna with a band notch characteristic is presented. The proposed antenna consists of two tridents and two uneven split ring resonators. The overall size of the antenna is 26 mm × 24 mm × 1.53 mm. By adding the uneven split ring resonators to the dual trident ultra-wideband antenna, a band notch of 5.05 GHz to 5.9 GHz is achieved. The band notch is adjusted by the size and the split locations of the resonators. CST microwave studios software was used to simulate the design. The measured |S₁₁| (dB) pass band and notch band agree with the simulation within the frequency band from 3.65 GHz to 12.85 GHz.